CFD modelling of supercritical water flow and heat transfer in a 2 x 2 fuel rod bundle

In the present assessment of the CFD code, two heat transfer experiments using water at supercritical pressures were selected: a 2 x 2 rod bare bundle; and a 2 x 2 rod wire-wrapped bundle. A systematic 3D CFD study of the fluid flow and heat transfer at supercritical pressures for the rod bundle geometries was performed with the key parameter being the fuel rod wall temperature. The sensitivity of the prediction to the steady RANS turbulence models of SST kappa-omega,nu(2)-f and turbulent Prandtl number (Pr-t) was tested to ensure the reliability of the predicted wall temperature obtained for the current analysis. Using the appropriate turbulence model based on the sensitivity analysis, the mesh refinement, or the grid convergence, was performed for the two geometries. Following the above sensitivity analyses and mesh refinements, the recommended CFD model was then assessed against the measurements from the two experiments. It was found that the CFD model adopted in the current work was able to qualitatively capture the trends reported by the experiments but the degree of temperature rise along the heated length was underpredicted. Moreover, the applicability of turbulence models varied case-by-case and the performance evaluation of the turbulence models was primarily based on its ability to predict the experimentally reported fuel wall temperatures. Of the two turbulence models tested, the SST kappa-omega was found to be better at capturing the measurements at pseudo-critical and supercritical test conditions, whereas the nu(2)-f performed better at sub-critical test conditions. Along with the appropriate turbulence model, CFD results were found to be particularly sensitive to the value of turbulent Prandtl number used in simulating the experimental test conditions for the bare and wire-wrapped fuel rod configuration. Crown Copyright (C) 2016 Published by Elsevier B.V. All rights reserved.